Abstract

Background

Although HIV-1 CRF12_BF and CRF38_BF are two epidemiologically important recombinant
lineages circulating in Argentina and Uruguay, little is known about their population
dynamics.

Methods

A total of 120 "CRF12_BF-like" and 20 "CRF38_BF-like" pol recombinant sequences collected in Argentina and Uruguay from 1997 to 2009 were subjected
to phylogenetic and Bayesian coalescent-based analyses to estimate evolutionary and
demographic parameters.

Results

Phylogenetic analyses revealed that CRF12_BF viruses from Argentina and Uruguay constitute
a single epidemic with multiple genetic exchanges among countries; whereas circulation
of the CRF38_BF seems to be confined to Uruguay. The mean estimated substitution rate
of CRF12_BF at pol gene (2.5 × 10-3 substitutions/site/year) was similar to that previously described
for subtype B. According to our estimates, CRF12_BF and CRF38_BF originated at 1983
(1978-1988) and 1986 (1981-1990), respectively. After their emergence, the CRF12_BF
and CRF38_BF epidemics seem to have experienced a period of rapid expansion with initial
growth rates of around 1.2 year-1 and 0.9 year-1, respectively. Later, the rate of spread of these CRFs_BF seems to have slowed down
since the mid-1990s.

Conclusions

Our results suggest that CRF12_BF and CRF38_BF viruses were generated during the 1980s,
shortly after the estimated introduction of subtype F1 in South America (~1975-1980).
After an initial phase of fast exponential expansion, the rate of spread of both CRFs_BF
epidemics seems to have slowed down, thereby following a demographic pattern that
resembles those previously reported for the HIV-1 epidemics in Brazil, USA, and Western
Europe.